Optical head with light-receiving device

ABSTRACT

The present invention realizes a compact and thin light-receiving device in a simple configuration, and provides a compact optical head on which this light-receiving device is mounted. The light-receiving device for receiving light reflected from an information recording medium includes a light-receiving chip having a plurality of electrodes and a flexible wiring board on which the light-receiving chip is mounted and fixed. The plurality of electrodes are connected electrically to the flexible wiring board by attaching directly or via a metal wire.

This application is a 371 of PCT/JP03/05668, filed May 6, 2003.

1. Technical Field

The present invention relates to an optical head for opticallyrecording/reproducing information with respect to an optical disk thatis an information recording medium.

2. Background Art

In the background of vigorous technical development of high density andlarge capacity memories, a rewriting function, in addition to highdensity, large capacity and high reliability, is an ability required formemories. Optical disks satisfy these requirements, and there is ademand for compact and simplified optical heads for opticallyrecording/reproducing information with respect to optical disks.

FIG. 7 is a schematic view showing a configuration of a general opticalhead. In FIG. 7, reference numeral 20 denotes an optical disk that is aninformation recording medium. Reference numeral 21 denotes asemiconductor laser that is a light source. Reference numeral 22 denotesan objective lens that is focusing means for focusing light emitted fromthe semiconductor laser 21 on the optical disk 20 as a small light spot.Reference numeral 23 denotes an objective lens actuator that is focusingdevice driving means for allowing the objective lens 22 to follow theside-runout or the decentering of the optical disk 20. Reference numeral24 denotes a half mirror for splitting light reflected from the opticaldisk 20. Reference numeral 25 denotes a light-receiving device forreceiving the light reflected from the optical disk 20. The optical head26 is composed of the semiconductor laser 21, the objective lens 22, theobjective lens actuator 23, the half mirror 24 and the light-receivingdevice 25. Thus, the light-receiving device 25 is a RF signallight-receiving device for detecting information signals of the opticaldisk 20, and also serves as a servo signal light-receiving device fordetecting servo signals thereof.

In the conventional commercial optical heads, a light-receiving devicedivided into multiple portions for detecting RF signals and detectingservo signals is used. FIGS. 8A and 8B show a simplified example of aconventional light-receiving device that is commonly used. FIGS. 8A and8B are a plan view and a cross-section view of a conventional halvedphotodiode that is a light-receiving device, respectively. Hereinafter,the configuration and the function of this halved photodiode will bedescribed. Reference numeral 30 denotes a halved photodiode that is alight-receiving device. Reference numerals 31 a and 31 b denotelight-receiving chips that are semiconductors (whose structure is notdescribed in detail) and have an area of 0.75 mm×0.75 mm and a thicknessof 0.3 mm. Reference numeral 38 denotes a divisional line that dividesthe light-receiving chips 31 a and 31 b. Reference numerals 32 a and 32b denote front face electrodes provided on the light-receiving chips 31a and 31 b, respectively. Reference numerals 33 a, 33 b, 33 c and 33 ddenote frame terminals. Reference numeral 34 denotes a frame in whichthe frame terminals 33 c and 33 d form an integral structure. Referencenumeral 35 denotes a back face electrode that is provided commonly tothe light-receiving chips 31 a and 31 b. Reference numeral 36 a denotesa metal wire for electrically connecting the electrode 32 a and theframe terminal 33 a. Reference numeral 36 b denotes a metal wire forelectrically connecting the electrode 32 b and the frame terminal 33 b.Reference numeral 37 denotes a resin for forming the halved photodiode30 as a light-receiving device in the shape of an area of 4 mm×5 mm,excluding the frame terminals, and a height of 1.8 mm.

The back face electrode 35 of the light-receiving chips 31 a and 31 b isconnected electrically to the frame 34. The front face electrodes 32 aand 32 b are connected electrically to the frame terminals 33 a and 33 bby the metal wires 36 a and 36 b. Therefore, the halved photodiode 30,which is a light-receiving device, has the frame terminals 33 a and 33 bas anode terminals, the frame terminals 33 c and 33 d as cathodeterminals and serves as a halved photodiode while the light received bythe light-receiving chips 31 a and 31 b is output from the frameterminals 33 a and 33 b, respectively, in the form of a photoelectriccurrent. For each size, substantial values are shown. The halvedphotodiode 30 that is a light-receiving device is a photodiode, so thatthe light-receiving chips 31 a and 31 b also can be referred to as“light-receiving cells”.

The halved photodiode 30 shown in FIGS. 8A and 8B, which is aconventional light-receiving device, has the following problems.

First, even if the light-receiving chips are small and thin, thelight-receiving device can be large and thick. In other words, althoughthe light-receiving chips 31 a and 31 b are small and thin, having anarea of 0.75 mm×0.75 mm and a thickness of 0.3 mm, the halved photodiode30 that is a light-receiving device is formed with a resin 37 having anarea of 4 mm×5 mm, excluding the frame terminals, and a height of 1.8mm.

Secondly, the flexible wiring board on which the halved photodiode 30 ismounted also can be large. This will be described with reference toFIGS. 9A and 9B. FIGS. 9A and 9B are a plan view and a cross-sectionalview showing the configuration in which the halved photodiode 30 shownin FIGS. 8A and 8B, which is a light-receiving device, is connectedelectrically to a flexible wiring board 48. In the halved photodiode 30,the frame terminals 33 a, 33 b, 33 c, and 33 d are connectedelectrically to conduction lines 39 on the flexible wiring board 48 bysoldering or the like. A component 40 is a reinforcing plate that isadhered to the flexible wiring board 48 so as to form an integral unitand is constituted by epoxy material containing glass. The flexiblewiring board 48 has an opening 47 larger than the 4 mm×5 mm outline ofthe resin 37 of the halved photodiode 30 in order to negate a step withthe frame terminals of the halved photodiode 30. Therefore, so-called“routing” of the conduction lines 39 cannot be performed withoutbypassing the outside of the resin 37 of the halved photodiode 30.Consequently, it cannot be avoided that the area of the periphery of amounting portion for the halved photodiode 30 of the flexible wiringboard 48 becomes large. In the case of the configuration shown in FIGS.9A and 9B, if the outline of the resin 37 is fit into the opening 47with a margin of 0.3 mm, the size of the opening 47 is 4.6 mm×5.6 mm.Furthermore, since the conduction lines 39 of the frame terminals 33 cand 33 d bypass the outside of the resin 37, the size of the flexiblewiring board 48 is 7.8 mm when it is assumed that the line width is 0.1mm and the space width is 0.5 mm.

Because of the first and the second problems as described above, theoptical head on which the halved photodiode 30 is mounted, which is alight-receiving device, has a problem in that the shape of the halvedphotodiode 30 is a factor of determining the size limit of the opticalhead. This will be described with reference to FIG. 10A. FIG. 10A is aside view of the optical head, and schematically shows the positionalrelationship of the optical disk 20, the semiconductor laser 21, whichis a light source, and the light-receiving device for detecting RFsignals and detecting servo signals.

As can be seen from FIG. 10A, assuming that the components are spacedaway from the optical disk 20 by 1 mm, since the diameter of thesemiconductor laser 21, which is a light source, is generally 5.6 mm,the light source portion can be arranged 6.6 mm from the optical disk20. On the other hand, in the case where the halved photodiode 30 shownin FIGS. 8A and 8B, which is a light-receiving device, is mounted andfixed to the flexible wiring board 48, as shown in FIGS. 9A and 9B, thesize of the flexible wiring board 48 of the detecting portion is 7.8 mm,as described above. The light-receiving device 30 is adjusted to bepositioned in a plane perpendicular to the optical axis so that theoptical head 26 can exhibit its performance, and it is assumed that themoving range thereof is ±0.5 mm. That is, the detecting portion requiresa space of 1 mm, a moving amount of 0.5 mm, a width of the flexiblewiring board 48 of 7.8 mm, and a moving amount of 0.5 mm, which makes9.8 mm from the optical disk 20. Thus, the detecting portion on whichthe light-receiving device 30 for detecting RF signals and detectingservo signals, which is essential to the optical head, is mounted, isprojected from the light source portion by as much as 3.2 mm, whichdetermines the size limit at least in the height direction of theoptical head.

Next, the case of a sensor for detecting, for example, a tilt of ainformation recording medium, instead of the light-receiving device fordetecting RF signals and detecting servo signals, which is essential tothe optical head, will be considered. Referring to FIG. 10B, the sensoris provided in parallel to the optical disk 20, for example, in a spaceabove the semiconductor laser 21, so as to detect a tilt of the opticaldisk 20. This sensor is the halved photodiode 30 that is thelight-receiving device shown in FIGS. 8A and 8B, and has a thickness of1.8 mm when it is mounted and fixed on the flexible wiring board 48 asshown in FIGS. 9A and 9B. That is, the light source portion requires aspace of 1 mm, a thickness of the sensor (halved photodiode 30, which isa light-receiving device) of 1.8 mm, and a size of the semiconductorlaser of 5.6 mm, which makes 8.4 mm from the optical disk 20. The sensorherein is not a light-receiving device for detecting RF signals anddetecting servo signals, which is essential to the optical head, andtherefore the enlarged size of 1.8 mm causes a large problem, especiallyin an attempt to achieve compact optical heads.

DISCLOSURE OF INVENTION

The present invention is carried out in light of the above problem, andit is an object of the present invention is to provide a compact andthin light-receiving device having a simple configuration, and toprovide a compact and thin optical head on which the light-receivingdevice is mounted.

In order to achieve the above object, a first optical head of thepresent invention includes a light source, means for driving a focusingelement, and a light-receiving device for receiving light reflected froman information recording medium, wherein the light-receiving devicecomprises a light-receiving chip having a plurality of electrodes, and aflexible wiring board on which the light-receiving chip is mounted andfixed, and the plurality of electrodes are connected electrically to theflexible wiring board by attaching directly or via a metal wire.

With this configuration, firstly, a light-receiving device that is morecompact and thinner than conventional light-receiving devices can berealized in a simple configuration without increasing the number of thecomponents. Secondly, the size of the flexible wiring board in which thelight-receiving device is configured can be reduced. Thirdly, a newoptical head in which a head flexible wiring board for electricalconnection of each component such as a light source or a light-receivingdevice is incorporated and fixed can be realized. Thus, as a whole, acompact optical head can be achieved.

In the first optical head, it is preferable that the light-receivingdevice is configured such that a protective resin for preventing damageis fixed to the flexible wiring board while covering only the metal wireor both the metal wire and the light-receiving chip. Thus, only themetal wire, which is the most susceptible to damage, or thelight-receiving surface side of the light-receiving chip as well as themetal wire, which is the most susceptible to damage, can be protectedfrom external damage, so that the light-receiving device can be handledmore easily.

In this case, it is preferable that the flexible wiring board is a partof a head flexible wiring board for connecting electrically between thelight source and the means for driving a focusing element, and anexternal circuit. Thus, the flexible wiring board is not a componentdedicated to the light-receiving device, so that an even more compactand simplified optical head can be achieved.

Furthermore, it is preferable that the light source is a light-emittingchip element, and the light-emitting chip element is connectedelectrically to the flexible wiring board by attaching directly or via ametal wire. Thus, the size of the optical head can be reduced, and thehead flexible wiring board can be simplified.

In order to achieve the above object, a second optical head of thepresent invention includes a light source, means for driving a focusingelement, a light-receiving device for receiving light reflected from aninformation recording medium, wherein the light-receiving devicecomprises a light-receiving chip having a plurality of electrodes, and amultilayered substrate with an internal conduction line on which thelight-receiving chip is mounted and fixed, and the plurality ofelectrodes are connected electrically to the multilayered substrate withan internal conduction line by attaching directly or via a metal wire.

With this configuration, the area of the light-receiving device is notincreased while utilizing the features of the multilayered substratewith an internal conduction line and the three-dimensionally arrangedelectrical conduction lines in a simple configuration without increasingthe number of the components. Therefore, firstly, a light-receivingdevice that is more compact and thinner than conventionallight-receiving devices can be realized. Secondly, the size of theflexible multilayered substrate with an internal conduction line inwhich the light-receiving device is configured can be reduced. Thirdly,a new optical head in which a head flexible wiring board for electricalconnection of each component such as a light source or a light-receivingdevice is incorporated and fixed can be realized, which will bedescribed later. Thus, as a whole, a compact optical head can beachieved.

In the second optical head, it is preferable that the light-receivingdevice is configured such that a protective resin for preventing damageis fixed to the multilayered substrate with an internal conduction linewhile covering only the metal wire or both the metal wire and thelight-receiving chip. Thus, only the metal wire, which is the mostsusceptible to damage, or the light-receiving surface side of thelight-receiving chip as well as the metal wire, which is the mostsusceptible to damage, can be protected from external damage, so thatthe light-receiving device can be handled more easily.

In this case, the multilayered substrate with an internal conductionline is connected electrically to a head flexible wiring board forelectrical connection of the light source and the means for driving afocusing element. Thus, the multilayered substrate with an internalconduction line is not a component dedicated to the light-receivingdevice, so that an even more compact and simplified optical head can beachieved.

Furthermore, it is preferable that the light source is a light-emittingchip element, and the light-emitting chip element is connectedelectrically to the head flexible wiring board by attaching directly orvia a metal wire. Thus, the size of the optical head can be reduced, andthe head flexible wiring board can be simplified.

Alternatively, it is preferable that the light source is alight-emitting chip element, and the light-emitting chip element isconnected electrically to a multilayered substrate with an internalconduction line that is the same as or different from the multilayeredsubstrate with an internal conduction line, by attaching directly or viaa metal wire. Thus, the light source and the light-receiving device areconfigured integrally as one unit as a so-called light-receiving andemitting element, so that an even more compact optical head can beachieved.

Furthermore, in the first and the second optical heads, it is preferablethat the light-receiving chip of the light-receiving device comprises alight-receiving cell on which light is incident, and a circuit portionfor amplifying and processing a photoelectric current from thelight-receiving cell. Thus, the output from the light-receiving cell isnot a photoelectric current, but a voltage output, including in the casewhere processing is performed, and more stable outputs can be obtainedfrom the optical head.

The present invention includes the case where the light-receiving celland the circuit portion are configured as totally separated elements. Inthis case, in the light-receiving chip of the light-receiving device, itis preferable that the light-receiving cell and the circuit portion areprovided independently from each other on front and back faces of theflexible wiring board for the first optical head, and the multilayeredsubstrate with an internal conduction line for the second optical head.Thus, even if the light-receiving device is a light-receiving deviceincorporating an electric circuit, the so-called radiation sensitivityof the light-receiving device can be increased, without increasing thearea of the light-receiving device.

In the first and the second optical heads, the light-receiving device isa RF signal detecting element for detecting an information signal of theinformation recording medium or a servo signal detecting element fordetecting a serve signal from the information recording medium. Thus,the size limit in the height direction of the optical head is notdetermined by the detecting portion.

Alternatively, the light-receiving device is a sensor used to detect atilt of the information recording medium or a tilt of the means fordriving a focusing element, or to confirm a light amount emitted fromthe light source. Thus, although a specific detecting sensor can beconfigured, the height or the size of the optical head is not increased.

In the first optical head, it is preferable that a light-receiving chipmounting portion of the flexible wiring board has a plurality ofparallel conduction lines, and the light-receiving chip is mounted onthe flexible wiring board such that a major division line issubstantially parallel to the plurality of conduction lines, and thatthe light-receiving chip is mounted substantially in the center of thelight-receiving chip mounting portion of the flexible wiring board.Thus, the advantage that the size limit in the height direction of theoptical head is not determined by the detecting portion can become morepronounced.

In the second optical head, it is preferable that a light-receiving chipmounting portion of the head flexible wiring board has a plurality ofparallel conduction lines, and the light-receiving chip mounted andfixed onto the multilayered substrate with an internal conduction lineis mounted on the head flexible wiring board such that a major divisionline is substantially parallel to the conduction lines, and that themultilayered substrate with an internal conduction line is mountedsubstantially in the center of the light-receiving chip mounting portionof the head flexible wiring board. Thus, the advantage that the sizelimit in the height direction of the optical head is not determined bythe detecting portion can become more pronounced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plan view showing an example of a configuration of a halvedlight-receiving device in an optical head according to Embodiment 1 ofthe present invention.

FIG. 1B is a cross-sectional view of the halved light-receiving deviceshown in FIG. 1A.

FIG. 2A is a side view of an optical head according to Embodiment 1 ofthe present invention, showing the positional relationship between theoptical disk and the light-receiving device for detecting RF signals anddetecting servo signals.

FIG. 2B is a side view of an optical head according to Embodiment 1 ofthe present invention, showing the positions of the optical disk and thelight-receiving device for detecting a tilt.

FIG. 3 is a plan view of the entire configuration of an optical headaccording to Embodiment 1 of the present invention, in the case wherethe flexible wiring board 48 is configured as a part of a head flexiblewiring board 50.

FIG. 4 is a plan view of the entire configuration of an optical headaccording to Embodiment 1 of the present invention, in the case wherethe semiconductor laser 21 of FIG. 3 is replaced by a light-emittingchip element 211.

FIG. 5A is a plan view showing an example of a configuration of a halvedlight-receiving device incorporating an electric circuit in an opticalhead according to Embodiment 2 of the present invention.

FIG. 5B is a cross-sectional view showing the halved light-receivingdevice incorporating an electric circuit of FIG. 5A.

FIG. 6 is a cross-sectional view showing in detail the multilayeredsubstrate on which the halved light-receiving device incorporating anelectric circuit of FIG. 5B is configured.

FIG. 7 is a schematic view showing the configuration of a generaloptical head.

FIG. 8A is a plan view showing the configuration of a halved photodiodethat is a light-receiving device in a conventional optical head.

FIG. 8B is a cross-sectional view of the halved photodiode shown in FIG.8A.

FIG. 9A is a plan view showing the configuration in which theconventional halved photodiode shown in FIGS. 8A and 8B is connectedelectrically to a flexible wiring board.

FIG. 9B is a cross-sectional view showing the configuration in which theconventional halved photodiode shown in FIGS. 8A and 8B is connectedelectrically to a flexible wiring board.

FIG. 10A is a side view of a conventional optical head, showing thepositional relationship between the optical disk and the light-receivingdevice for detecting RF signals and detecting servo signals.

FIG. 10B is a side view of a conventional optical head, showing thepositional relationship of the optical disk and the light-receivingdevice for detecting a tilt.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference of the accompanying drawings.

Embodiment 1

FIGS. 1A and 1B are a plan view and a cross-sectional view showing anexample of a configuration of a halved light-receiving device in anoptical head according to Embodiment 1 of the present invention, and theconfiguration and the function thereof will be described below. Thelight-receiving device of FIGS. 1A and 1B can be used as a component ofthe optical head, as in the case of the light-receiving device 25 of thegeneral optical head shown in FIG. 7.

In FIGS. 1A and 1B, reference numerals 31 a and 31 b denotelight-receiving chips that are semiconductors (whose structure is notdescribed in detail) and have an area of 0.75 mm×0.75 mm and a thicknessof 0.3 mm. Reference numeral 38 denotes a division line that divides thelight-receiving chips 31 a and 31 b. Reference numerals 32 a and 32 bdenote front face electrodes provided on the light-receiving chips 31 aand 31 b, respectively. Reference numeral 35 denotes a back faceelectrode that is provided commonly to the light-receiving chips 31 aand 31 b. Reference numeral 48 denotes a flexible wiring board.Reference numerals 39 a, 39 b and 39 c denote conduction lines on theflexible wiring board. Reference numeral 40 denotes a reinforcing platethat is made of epoxy material containing glass and is adhered to theflexible wiring board 48 so as to form an integral unit. Referencenumeral 36 a denotes a metal wire for electrically connecting theelectrode 32 a and the conduction line 39 a. Reference numeral 36 bdenotes a metal wire for electrically connecting the electrode 32 b andthe conduction line 39 b. Reference numerals 42 a and 42 b denoteprotective resins for covering the metal wires 36 a and 36 b and beingfixed to the flexible wiring board 48. These components above constitutea halved light-receiving device 43.

The light-receiving chips 31 a and 31 b are connected electrically tothe conduction line 39 c of the flexible wiring board 48 with the backelectrode 35. The front face electrodes 32 a and 32 b are connectedelectrically to the conduction lines 39 a and 39 b of the flexiblewiring board 48 by the metal wires 36 a and 36 b, respectively. Theprotective resins 42 a and 42 b are resins that can be cured byultraviolet rays, and can prevent damage or breakage of the metal wires36 a and 36 b, which exhibit the function of electrical connection.Therefore, the halved light-receiving device 43 has the conduction lines39 a and 39 b as anode terminals, the conduction line 39 c as a cathodeterminal and serves as a so-called halved photodiode while the lightreceived by the light-receiving chips 31 a and 31 b is output to theconduction lines 39 a and 39 b, respectively, in the form of aphotoelectric current. For each size, substantial values are shown. Thehalved light-receiving device 43 is a photodiode, so that thelight-receiving chips 31 a and 31 b also can be referred to as“light-receiving cells”. Herein, other elements or functions thatconstitute the optical head but are not relevant to the presentinvention are not shown or described.

Thus, in Embodiment 1 of the present invention, when comparing thehalved light-receiving device 43 of FIGS. 1A and 1B with theconventional configuration shown in FIGS. 9A and 9B, the embodiment ofthe present invention firstly can realize a compact and thin halvedlight-receiving device 43 without increasing the number of thecomponents and secondly also can realize a compact flexible wiring boardon which the halved light-receiving device 43 is configured. Therefore,the present invention can provide an excellent effect that an opticalhead on which they are mounted can be compact.

Referring to more specific values, in FIG. 1A, when it is assumed thatthe space width between the conduction lines 39 a and 39 b and theoutline of the flexible wiring board 48 is 0.5 mm, the size of theflexible wiring board 48 is 2.5 mm, whereas the size in the longitudinaldirection (direction perpendicular to the division line 38) of thelight-receiving chips 31 a and 31 b is 1.5 mm. The outline of theflexible wiring board 48 is projected from the light-receiving chips 31a and 31 b only by about 0.5 mm in the upper right end portion in thedrawing.

FIG. 2A is a side view of the optical head and schematically shows thepositional relationship between the optical disk 20, the semiconductorlaser 21, which is a light source, and the light-receiving device 43 fordetecting RF signals and detecting servo signals shown in FIGS. 1A and1B of this embodiment. As can be seen from FIG. 2A, assuming that thecomponents are spaced apart from the optical disk 20 by 1 mm, when thelight-receiving device 43 of the detecting portion is the halvedphotodiode shown in FIGS. 1A and 1B, the size of the flexible wiringboard 48 of the detecting portion is 2.5 mm, as described above. Thelight-receiving device 43 is adjusted so as to be positioned in a planeperpendicular to the optical axis so that the optical head can exhibitits performance, and it is assumed that the moving range thereof is ±0.5mm. That is, the detecting portion requires a space of 1 mm, a movingamount of 0.5 mm, a width of the flexible wiring board 48 of 2.5 mm, anda moving amount of 0.5 mm, which makes 4.5 mm from the optical disk 20.Thus, the detecting portion on which the light-receiving device 43 fordetecting RF signals and detecting servo signals, which is essential tothe optical head, is mounted is not projected from the light sourceportion, unlike the conventional example shown in FIG. 10A. In otherwords, the size limit in the height direction of the optical head is notdetermined by the detecting portion.

Next, the case of a sensor for detecting, for example, a tilt of ainformation recording medium, instead of the light-receiving device fordetecting RF signals and detecting servo signals is mounted, which isessential to the optical head, will be considered. Referring to FIG. 2B,the sensor is provided in parallel to the optical disk 20 so as todetect a tilt of the optical disk 20, for example, in a space above thelight-receiving device 43 for detecting RF signals and detecting servosignals. When this sensor is a halved photodiode that is thelight-receiving device shown in FIGS. 1A and 1B, its thickness is 1.0mm. That is, the detecting portion requires a space of 1 mm, a thicknessof the sensor (halved photodiode that is a light-receiving device) of1.0 mm, a moving amount of 0.5 mm, a width of the flexible wiring board48 of 2.5 mm, and a moving amount of 0.5 mm, which makes 5.5 mm from theoptical disk 20. Since this is smaller than the size of the light sourceportion of 6.6 mm, a tilt detecting sensor of the optical disk 20 can beconfigured without increasing the height of the optical head.

In this embodiment, the protective resins 42 a and 42 b are fixed to theflexible wiring board 48 while covering the metal wires 36 a and 36 b,but they may be fixed to the flexible wiring board 48 while covering thelight-receiving chips 31 a and 31 b on the side of the light-receivingsurface as well as the metal wires 36 a and 36 b. In this configuration,not only the metal wires 36 a and 36 b, which are the most susceptibleto damage, but also the light-receiving surface of the light-receivingchips 31 a and 31 b can be protected from external damage, so that thehalved light-receiving device 43 can be handled more easily.

In this embodiment, in the flexible wiring board 48, only the peripheralportion of the halved light-receiving device 43 is shown for example,but the flexible wiring board 48 may be a part of a head flexible wiringboard for electrical connection of a light source or means for driving alight focusing element. FIG. 3 is a plan view of the entireconfiguration of an optical head according to Embodiment 1 of thepresent invention, in the case where the flexible wiring board 48 isconfigured as a part of a head flexible wiring board 50. In FIG. 3, thehead flexible wiring board 48 is a part of the head flexible wiringboard 50 for electrical wiring between a semiconductor laser 21, anobjective lens actuator 23 for driving an objective lens 22 and thehalved light-receiving device 43 and an external circuit. Thus, theflexible wiring board 48 is not a component dedicated to the halvedlight-receiving device 43, so that an even more compact and simplifiedoptical head can be achieved. This is because a method for connectingelectrically the head flexible wiring board and the components or amethod for arranging the head flexible wiring board itself in theoptical head (method for routing conduction lines) can be simplified.

As shown in FIG. 4, the light source may be a light-emitting chipelement 211, and the light-emitting chip element 211 may be connectedelectrically to the flexible wiring board 48 by attaching directly orvia a metal wire. In other words, the light source is not thesemiconductor laser 21 that is packaged with a diameter of 5.6 mm asshown in FIG. 2A, but a semiconductor chip that emits light and has asize of less than 1 mm³ as shown in FIG. 4 is connected electrically tothe flexible wiring board, so that a compact optical head and asimplified head flexible wiring board can be achieved.

In this embodiment, the halved light-receiving device 43 is assumed tobe a photodiode, as understood from the fact that the light-receivingchips 31 a and 31 b are referred to as “light-receiving cells”. However,each of the light-receiving chips 31 a and 31 b may be a light-receivingdevice incorporating an electric circuit that is constituted by alight-receiving cell to which light is incident and a circuit portionfor amplifying and processing a photoelectric current from thelight-receiving cell. In this case, the output from the light-receivingcells is not a photoelectric current, but a voltage output, includingthe case where processing is performed. Thus, more stable outputs can beobtained from the optical head.

In this embodiment, the case where the halved light-receiving device 43is a RF signal detecting element for detecting information signals of aninformation recording medium or a servo signal detecting element fordetecting serve signals from an information recording medium, or asensor for detecting of a tilt of an information medium has beendescribed for example. However, the halved light-receiving device 43 canbe any light-receiving device that can be used in an optical head, suchas a sensor used to detect a tilt of means for driving a focusingelement or to confirm the light amount emitted from a light source.

In this embodiment, as shown in FIG. 1A, the light-receiving chipmounting portion of the light-receiving device 43 of the flexible wiringboard 48 is configured to have a size of 2.5 mm, which is about the samesize as the length of the longitudinal side of the light-receiving chips31 a and 31 b, which is 1.5 mm, as opposed to the conventional exampleshown in FIG. 9A. Thus, as shown in FIG. 2A, the size limit in theheight direction of the optical head is not determined by the detectingportion.

Furthermore, in this embodiment, as shown in FIG. 1A, thelight-receiving chip mounting portion of the light-receiving device 43of the flexible wiring board 48 has three parallel conduction lines 39a, 39 b and 39 c, and the light-receiving chips 31 a and 31 b aremounted on the flexible wiring board 48 such that the major divisionline 38 is substantially parallel to these conduction lines. Inaddition, the light-receiving chips 31 a and 31 b are mountedsubstantially in the center of the flexible wiring board 48. Thisconfiguration can make the advantage that the size limit in the heightdirection of the optical head is not determined by the detecting portionmore pronounced, as shown in FIG. 2A.

As described above, by developing the configuration of this embodimentshown in FIGS. 1A and 1B, not only can the size of the halvedlight-receiving device 43, which is a light-receiving device, be reducedin the peripheral portion, but also a new optical head in which a headflexible wiring board for electrical connection of each component suchas a light source or a light-receiving device is incorporated and fixedcan be configured.

Embodiment 2

FIGS. 5A and 5B are a plan view and a cross-sectional view showing ahalved light-receiving device incorporating an electric circuit in theoptical head according to Embodiment 2 of the present invention, and theconfiguration and the function thereof will be described below. Thehalved light-receiving device incorporating an electric circuit of FIGS.5A and 5B can be used as a component of the optical head, as in the caseof the light-receiving device 25 of the general optical head shown inFIG. 7.

In FIGS. 5A and 5B, reference numerals 41 a and 41 b denotelight-receiving cells that are semiconductors (whose structure is notdescribed in detail) and have an area of 0.75 mm×0.75 mm and a thicknessof 0.3 mm. Reference numeral 38 denotes a division line that divides thelight-receiving cells 41 a and 41 b. Reference numerals 32 a and 32 bdenote front face electrodes provided on the light-receiving cells 41 aand 41 b, respectively. Reference numeral 35 denotes a back faceelectrode that is provided commonly to the light-receiving cells 41 aand 41 b. Reference numeral 44 denotes a multilayered substrate with aninternal conduction line, on a plane P of which the light-receivingcells 41 a and 41 b are mounted and fixed. Reference numerals 45 a and45 b denote metal leads provided on the multilayered substrate 44 withan internal conduction line. Reference numeral 36 a denotes a metal wirefor electrically connecting the electrode 32 a and the metal lead 45 a.Reference numeral 36 b denotes a metal wire for electrically connectingthe electrode 32 b and the metal lead 45 b. Reference numerals 42 a and42 b denote protective resins for covering the metal wires 36 a and 36 band being fixed to the multilayered substrate 44 having an internalconduction line. Reference numeral 46 denotes a circuit portion foramplifying and processing a photoelectric current from thelight-receiving cells 41 a and B41 b, and is connected electrically to,and mounted on and fixed to a plane Q that is the back face of themultilayered substrate 44 with an internal conduction line with respectto the light-receiving cells 41 a and 41 b. The above-describedcomponents constitute a halved light-receiving device 43 incorporatingan electric circuit that is a light-receiving device. In thisembodiment, the light-receiving chip is constituted by thelight-receiving cells 41 a and 41 b and the circuit portion 46.Reference numeral 48 denotes a flexible wiring board for electricallyconnecting, and mounting and fixing the multilayered substrate 44 withan internal conduction line. Reference numeral 40 denotes a reinforcingplate that is made of epoxy material containing glass and is adhered tothe flexible wiring board 48 so as to form an integral unit. Referencenumerals 42 a and 42 b denote resins that can be cured by ultravioletrays, and can prevent damage or breakage of the metal wires 36 a and 36b that carry out the function of electrical connection.

The light-receiving cells 41 a and 41 b are connected electrically tothe metal lead (not shown) on the plane P of the multilayered substrate44 with an internal conduction line via the back face electrode 35. Thefront face electrodes 32 a and 32 b are connected electrically to themetal leads 45 a and 45 b of the multilayered substrate 44 with aninternal conduction line by the metal wires 36 a and 36 b, respectively.In the internal structure of the multilayered substrate 44 provided withan internal conduction line, a plurality of layers that are providedwith metal wires are stacked and electrical connection between thelayers is established by metal holes, so that in the multilayeredsubstrate 44 with an internal conduction line, electric wiring isperformed three-dimensionally, including the portion between the plane Pof the front face and the plane Q of the back face.

As the multilayered substrate 44 with an internal conduction line, amultilayered ceramic substrate or a multilayered print substrate can beused. When a multilayered ceramic substrate is used, an advantage ofeasy processing and molding can be provided. When a multilayered printsubstrate is used, an advantage of excellent mass productivity can beprovided.

In the halved light-receiving device 43 incorporating an electriccircuit, which is a light-receiving device, the light received by thelight-receiving cells 41 a and 41 b arranged on the plane P flows in theform of a photoelectric current from the metal leads 45 a and 45 bthrough the electrical conduction lines (not shown) inside themultilayered substrate 44 with an internal conduction line to thecircuit portion 46 on the plane Q of the back face of the multilayeredsubstrate 44 with an internal conduction line. A plurality of electrodes(not shown) of the circuit portion 46 are connected electrically to aplurality of metal leads (not shown) provided on the plane Q of themultilayered substrate 44 with an internal conduction line by, forexample, a bump method. In this circuit portion 46, the photoelectriccurrent from the light-receiving cells 41 a and 41 b is amplified andprocessed so that electric signals necessary to the optical head areoutput as a voltage. All the electric signals that are output as avoltage and the electric signals necessary to operate the circuitportion 46 are input and output through the plurality of metal leads(not shown) provided on the plane Q of the multilayered substrate 44with an internal conduction line and the electrical conduction linesprovided on the plane Q by the conduction lines (not shown) of theflexible wiring board 48. The electrical conduction lines provided onthe plane Q of the multilayered substrate 44 with an internal conductionline and the conduction lines of the flexible wiring board 48 areconnected electrically to each other in the contact portion of the planeQ and the flexible wiring board 48 by, for example, a bump method.Herein, other elements or functions that constitute the optical head butare not relevant are not shown or described.

FIG. 6 is a cross-sectional view showing in detail the multilayeredsubstrate in which the halved light-receiving device incorporating anelectric circuit of FIG. 5B is configured. In FIG. 6, thelight-receiving cells 41 a and 41 b are arranged in a recess in theuppermost layer, unlike those in FIG. 5B. The multilayered substrate 44is constituted by laminating layers 441 including a metal wire 441L, andelectrical connection of the layers is established via a metal hole 442.Reference numeral 49 denotes a surface mounted component that is mountedon the same surface as the circuit portion 46.

Thus, in this embodiment, when comparing the halved light-receivingdevice 43 incorporating an electric circuit, which is a light-receivingdevice, shown in FIGS. 5A and 5B with the conventional configurationshown in FIGS. 9A and 9B, the embodiment of the present inventionfirstly can realize a compact and thin light-receiving device 43 withoutincreasing the number of the components and secondly also can realize acompact flexible wiring board 48 on which the light-receiving device 43is mounted.

Referring to more specific values, in FIG. 5A, when it is assumed thatthe space width with respect to the outline of the multilayeredsubstrate 44 with an internal conduction line is 0.5 mm, the size of themultilayered substrate 44 with an internal conduction line is 2.5 mm,whereas the size in the longitudinal direction (direction perpendicularto the division line 38) of the light-receiving cells 41 a and 41 b is1.5 mm. The size in the longitudinal direction (direction perpendicularto the division line 38) of the flexible wiring board 48 can be smallerthan the size of the multilayered substrate 44 with an internalconduction line. Therefore, the size in the longitudinal direction(direction perpendicular to the division line 38) of the halvedlight-receiving device 43 incorporating an electric circuit, which is alight-receiving device, can be 2.5 mm. Consequently, the specific sizeof a compact optical head is such that the detecting portion ispositioned with 4.5 mm from the optical disk 20, as described inEmbodiment 1 referring to FIG. 2A. The detecting portion on which thelight-receiving device 43 for detecting RF signals and detecting servosignals, which is essential to the optical head, is mounted is notprojected from the light source portion, unlike the conventional exampledescribed referring to FIG. 10A. In other words, the size limit in theheight direction of the optical head is not determined by the detectingportion.

Thus, although this embodiment is a light-receiving device 43incorporating an electric circuit of a type in which the light-receivingcells 41 a and 41 b and the circuit portion 46 are configured as totallyseparate elements, the multilayered substrate 44 with an internalconduction line and its three-dimensionally arranged electricalconduction lines prevent the area of the light-receiving device fromincreasing. Therefore, an excellent effect can be obtained in that acompact optical head on which they are mounted can be realized.Furthermore, since this is a halved light-receiving device 43incorporating an electric circuit, the output from the light-receivingcells 41 a and 41 b is a voltage output, including the case whereprocessing is performed, and thus more stable outputs can be obtainedfrom the optical head. Moreover, although this embodiment is alight-receiving device 43 incorporating an electric circuit, it is not atype in which the light-receiving cells and the circuit portion areconfigured on the same semiconductor substrate, but the light-receivingcells 41 a and 41 b and the circuit portion 46 are configured as totallyseparate elements. Therefore, an effect can be obtained in thatso-called the radiation sensitivity of the light-receiving device can beincreased. This can solve the problem that the radiation sensitivity ofa photo IC is about 80% of that of a photodiode.

In this embodiment, the protective resins 42 a and 42 b are fixed to themultilayered substrate 44 having an internal conduction line whilecovering the metal wires 36 a and 36 b, but they can be fixed to themultilayered substrate 44 having an internal conduction line whilecovering the light-receiving cells 41 a and 41 b on the side of thelight-receiving surface as well as the metal wires 36 a and 36 b. Inthis configuration, not only the metal wires 36 a and 36 b, which arethe most susceptible to damage, but also the light-receiving surface ofthe light-receiving cells 41 a and 41 b can be protected from externaldamage, so that the halved light-receiving device 43 incorporating anelectric circuit, which is a light-receiving device, can be handled moreeasily.

In this embodiment, in the flexible wiring board 48, only the peripheralportion of the halved light-receiving device 43 incorporating anelectric circuit, which is a light-receiving device, is shown forexample, but the flexible wiring board 48 can be a part of a headflexible wiring board for electrical connection of a light source ormeans for driving a light focusing element. More specifically, theflexible wiring board 48 is a part of a head flexible wiring board (notshown) for electrical wiring between a semiconductor laser 21, anobjective lens actuator 23 and the light-receiving device 25 of theoptical head 26 of FIG. 3 and an external circuit, and is not acomponent dedicated to the halved light-receiving device 43incorporating an electric circuit, which is a light-receiving device.Therefore, an even more compact and simplified optical head can beachieved.

This is because a method for connecting electrically the head flexiblewiring board and the components or a method for arranging the headflexible wiring board itself in the optical head (method for routingconduction lines) can be simplified. In this case, the light source maybe a light-emitting chip element, and the light-emitting chip elementmay be connected electrically to the head flexible wiring board byattaching directly or via a metal wire. In other words, the light sourceis not the semiconductor laser 21 that is packaged with a diameter of5.6 mm as shown in FIG. 2A, but a semiconductor chip that emits lightand has a size of less than 1 mm³ as shown in FIG. 4 referred to inEmbodiment 1 is connected electrically to the head flexible wiringboard, so that a compact optical head and a simplified head flexiblewiring board can be achieved.

Furthermore, the light source may be a light-emitting chip element, andthe light-emitting chip element may be connected electrically to amultilayered substrate with an internal conduction line that is the sameas or different from the multilayered substrate 44 with an internalconduction line on which a light-receiving device is configured, byattaching directly or via a metal wire. For example, when the lightsource is not the semiconductor laser 21 that is packaged with adiameter of 5.6 mm as shown in FIG. 2A, but a semiconductor chip thatemits light and has a size of less than 1 mm³ is connected electricallyto the multilayered substrate 44 having an internal conduction line,then the light source and the light-receiving device are configuredintegrally as one unit as a so-called light-receiving and emittingelement, so that an even more compact optical head can be achieved.

In this embodiment, the halved light-receiving device 43 incorporatingan electric circuit is configured so as to have the light-receivingcells 41 a and 41 b and the circuit portion 46, but as expressed that alight-receiving chip is constituted by the light-receiving cells 41 aand 41 b and the circuit portion 46, the halved light-receiving device43 incorporating an electric circuit may be a halved photodiode that isa light-receiving device having only the light-receiving cells 41 a and41 b without the circuit portion 46.

In this embodiment, the case where the halved light-receiving device 43is a RF signal detecting element for detecting information signals of aninformation recording medium or a servo signal detecting element fordetecting servo signals from an information recording medium has beendescribed for example. However, the halved light-receiving device 43 maybe any light-receiving device that can be used in an optical head, suchas a sensor used to detect a tilt of an information recording medium ora tilt of means for driving a focusing element, or to confirm the lightamount emitted from a light source. In this case as well, the height ofthe optical head is not increased.

In this embodiment, as shown in FIG. 5A, the light-receiving chipmounting portion of the light-receiving device 43 of the multilayeredsubstrate 44 with an internal conduction line is configured to have asize of 2.5 mm, which is about the same size as the length of thelongitudinal side of the light-receiving chips 31 a and 31 b, which is1.5 mm, as opposed to the conventional example shown in FIG. 9A. Thus,similarly to Embodiment 1 described with reference to FIG. 2A, the sizelimit in the height direction of the optical head is not determined bythe detecting portion.

Furthermore, in this embodiment, as shown in FIG. 5A, the mountingportion for the light-receiving device 43 of the head flexible wiringboard 48 has three parallel conduction lines 39, and the light-receivingcells 41 a and 41 b are mounted on the multilayered substrate 44 with aninternal conduction line such that the major division line 38 issubstantially parallel to these conduction lines 39. In addition, thelight-receiving cells 41 a and 41 b are mounted substantially in thecenter of the multilayered substrate 44 with an internal conductionline. This configuration can make more pronounced the advantage that thesize limit in the height direction of the optical head is not determinedby the detecting portion, similarly to Embodiment 1 described withreference to FIG. 2A.

As described above, by developing the configuration of this embodimentshown in FIGS. 5A and 5B, not only is it possible to reduce the size ofonly the peripheral portion of the halved light-receiving device 43,which is a light-receiving device, but also a new optical head in whicha head flexible wiring board for electrical connection of each componentsuch as a light source or a light-receiving device is incorporated andfixed can be configured.

As described above, first, the present invention can realize alight-receiving device that is more compact and thinner thanconventional examples in a simple configuration without increasing thenumber of the components, secondly can achieve a compact flexible wiringboard or multilayered substrate with an internal conduction line onwhich a light-receiving device is configured, and thirdly can realize anew optical head in which a head flexible wiring board for electricalconnection of each component such as a light source or a light-receivingdevice is incorporated and fixed. Thus, as a whole, a compact opticalhead can be achieved.

1. An optical head comprising a light source, means for driving afocusing element, and a light-receiving device for receiving lightreflected from an information recording medium, wherein thelight-receiving device comprises a light-receiving chip having aplurality of electrodes, and a flexible wiring board on which thelight-receiving chip is mounted and fixed, the plurality of electrodesare connected electrically to the flexible wiring board by attachingdirectly or via a metal wire, the light-receiving chip of thelight-receiving device comprises a light-receiving cell on which lightis incident and a circuit portion for amplifying and processing aphotoelectric current from the light-receiving cell, and thelight-receiving cell and the circuit portion are provided independentlyfrom each other on a front face and a back face of the flexible wiringboard.
 2. The optical head according to claim 1, wherein thelight-receiving device is configured such that a protective resin forpreventing damage is fixed to the flexible wiring board while coveringonly the metal wire or both the metal wire and the light-receiving chip.3. The optical head according to claim 1, wherein the flexible wiringboard is a part of a head flexible wiring board for connectingelectrically between the light source and the means for driving afocusing element, and an external circuit.
 4. The optical head accordingto claim 3, wherein the light source is a light-emitting chip element,and the light-emitting chip element is connected electrically to theflexible wiring board by attaching directly or via a metal wire.
 5. Theoptical head according to claim 1, wherein the light-receiving device isa RF signal light-receiving device for detecting an information signalof the information recording medium or a servo signal light-receivingdevice for detecting a servo signal from the information recordingmedium.
 6. The optical head according to claim 1, wherein thelight-receiving device is a sensor used to detect a tilt of theinformation recording medium or a tilt of the means for driving afocusing element, or to confirm a light amount emitted from the lightsource.
 7. The optical head according to claim 1, wherein alight-receiving chip mounting portion of the flexible wiring board has aplurality of parallel conduction lines, and the light-receiving chip ismounted on the flexible wiring board such that a major division line issubstantially parallel to the plurality of conduction lines.
 8. Theoptical head according to claim 7, wherein the light-receiving chip ismounted substantially in the center of the light-receiving chip mountingportion of the flexible wiring board.
 9. An optical head comprising alight source, means for driving a focusing element, and alight-receiving device for receiving light reflected from an informationrecording medium, wherein the light-receiving device comprises alight-receiving chip having a plurality of electrodes, and amultilayered substrate with an internal conduction line on which thelight-receiving chip is mounted and fixed, and the plurality ofelectrodes are connected electrically to the multilayered substrate withan internal conduction line by attaching directly or via a metal wire.10. The optical head according to claim 9, wherein the light-receivingdevice is configured such that a protective resin for preventing damageis fixed to the multilayered substrate with an internal conduction linewhile covering only the metal wire or both the metal wire and thelight-receiving chip.
 11. The optical head according to claim 9, whereinthe multilayered substrate with an internal conduction line is connectedelectrically to a head flexible wiring board for connecting electricallybetween the light source and the means for driving a focusing element,and an external circuit.
 12. The optical head according to claim 11,wherein the light source is a light-emitting chip element, and thelight-emitting chip element is connected electrically to the headflexible wiring board by attaching directly or via a metal wire.
 13. Theoptical head according to claim 11, wherein the light source is alight-emitting chip element, and the light-emitting chip element isconnected electrically to a multilayered substrate with an internalconduction line that is the same as or different from the multilayeredsubstrate with an internal conduction line, by attaching directly or viaa metal wire.
 14. The optical head according to claim 11, wherein alight-receiving chip mounting portion of the head flexible wiring boardhas a plurality of parallel conduction lines, and the light-receivingchip mounted and fixed onto the multilayered substrate with an internal.conduction line is mounted on the head flexible wiring board such that amajor division line is substantially parallel to the plurality ofconduction lines.
 15. The optical head according to claim 14, whereinthe multilayered substrate with an internal conduction line is mountedsubstantially in the center of the light-receiving chip mounting portionof the head flexible wiring board.
 16. The optical head according toclaim 9, wherein the light-receiving chip of the light-receiving devicecomprises a light-receiving cell on which light is incident and acircuit portion for amplifying and processing a photoelectric currentfrom the light-receiving cell.
 17. The optical head according to claim16, wherein the light-receiving cell and the circuit portion areprovided independently from each other on a front face and a back faceof the multilayered substrate with an internal conduction line.
 18. Theoptical head according to claim 9, wherein the light-receiving device isa RF signal light-receiving device for detecting an information signalof the information recording medium or a servo signal light-receivingdevice for detecting a servo signal from the information recordingmedium.
 19. The optical head according to claim 9, wherein thelight-receiving device is a sensor used to detect a tilt of theinformation recording medium or a tilt of the means for driving afocusing element, or to confirm a light amount emitted from the lightsource.